New Hams often ask “What’s the difference between 2 meter and 70 centimeter, (or 144 Mhz/VHF vs. 440 Mhz/UHF)?” when choosing a first radio. It’s a great question, so I thought I’d address that today.
A few basic things come to mind:
- Hams have “Primary” operating authority in the 2 meter band, meaning other users in this range have to move if they are creating interference.
- Hams have “Secondary” operating authority in the 70 centimeter band, meaning we have to move if we are creating interference to the primary user. Practically speaking, here in the San Francisco Bay Area, the military is the primary user in the 440 Mhz frequency spectrum, so many amateur repeaters have been forced off the air in the past decade for causing interference to the primary user due to a change in configuration and usage of PAVE/PAWS, an early missile warning system operating out of Fort Beale.
- 144-148 Mhz is a relatively limited slice of spectrum, with only 4 Mhz.
- 420-450 Mhz is a wide slice of spectrum (30 Mhz) so there is more room, albeit with serious restrictions and the secondary allocation problem.
- Often, there are more choices for 2 meter equipment, including a number of mono-band radios.
- However, dual band radios offering both 144 Mhz and 440 Mhz capabilities are often practically the same price.
Perhaps more importantly, VHF radio, or the 144 Mhz range travels father in outdoor situations, while UHF or the 440 Mhz range operates better indoors. Because the wavelength of 70 centimeter is shorter, it does a better job of penetrating buildings. VHF also has the unique characteristic of sort of “hugging the terrain.” Practically speaking this means if you are a few feet below the crest of a hill that is between you and the transmitter, you might hear it better on VHF than on UHF.
A visual example helps here. I mapped the VHF and UHF ranges from my home in San Francisco, using the same antenna gain and same power output. Green shows as strong coverage, yellow shows as weaker coverage. This is for 50 watts out, with a 4db gain antenna at 6 meter height fed by low loss co-axial cable.
First, the VHF (144 Mhz) Map: (click on the map for an enlarged view in a new browser tab)
Now the UHF (440 Mhz) Map: (click on the map for an enlarged view in a new browser tab)
My home is a pretty interesting example, because while I live in an urban center, I also live in a small canyon. Consequently, you can see clear shadows where line of site radio transmission breaks down, particularly in the UHF map. I live in the shadow of the Merced Heights and the San Bruno range, giving my reception pattern mostly an east-west pattern, with limited, north/south visibility.
The upshot, is with most things being equal, I can generally get better coverage and reach more repeaters with VHF than with UHF. This is why you often see wide area repeaters and interties that cover large geographic regions in the VHF spectrum instead of the UHF spectrum.
Interesting, isn’t it...